Process for hydrogenating unsaturated compounds in c3-hydrocarbon fractions

ABSTRACT

Process for the complete saturation of a stream containing C2 to C4 hydrocarbons by hydrogenating such in a trickle phase over a fixed bed noble metal catalyst in the presence of a hydrogen atmosphere wherein about 0.3 to 3 parts of hydrogenation products per part of fresh feed are recycled in the process.

United States Patent [72] Inventors Walter Kronig Leverkusen; Wilhelm Mayrholer, Leverkusen; Gerhard Scharfe, Leverkusen; Kurt Halcour, Cologne-Stammheim, all of Germany [21] Appl. No. 858,548

Continuation of application Ser. No. 545,553, Apr. 27, 1966, now abandoned.

[54] PROCESS FOR HYDROGENATING UNSATURATED COMPOUNDS IN C 3 HYDROCARBON FRACTIONS 3 Claims, No Drawings [52] U.S. Cl 260/683.9, 208/143 [51] Int. Cl C07c 5/04 [50] Field of Search 260/6839, 677; 208/143 144, 216, 217, 255,257,264

[56] References Cited UNITED STATES PATENTS 3,075,917 1/1963 Kronig et a]. 208/255 3,167,498 1/1965 Kronig et al. 208/143 Primary Examiner-Herbert Levine Attorney-Burgess, Dinklage & Sprung ABSTRACT: Process for the complete saturation of a stream containing C to C hydrocarbons by hydrogenating such in a trickle phase over a fixed bed noble metal catalyst in the presence of a hydrogen atmosphere wherein about 0.3 to 3 parts of hydrogenation products per part of fresh feed are recycled in the process.

PRQCESS FOR HYDROGENATING UNSATURATED O N S 1N QrHYDBQQABBQN i ERAQIIQNS This application is a continuation of Ser. No. 545,553 filed Apr. 27, 1966 now abandoned.

This invention relates to a process for hydrogenating unsaturated compounds in c -hydrocarbon fractions.

When gaseous or liquid hydrocarbons are converted thermally or catalytically, hydrocarbon fractions with three carbon atoms in the molecule are obtained, these fractions containing varying quantities of unsaturated compounds, mainly propylene, but possibly also more strongly unsaturated compounds. The content of propylene in these C -fractions is generally between 35 percent and 95 percent by volume. If the conversion of the hydrocarbons being used is carried out at relatively high temperatures, especially above 600 C. but in particular between 700 and 900 C., the C -fractions which are formed also contain methyl acetylene and propadiene in quantities between 0.1 percent and percent in addition to propylene and propane. The C -fractions obtained in the conversion processes are now not suitable for direct use for all purposes. For some purposes, the more highly unsaturated compounds (methyl acetylene, propadiene) are disturbing. ln these cases, it is possible by means of known processes to convert these undesired constituents by selective hydrogenation into propylene and propane, respectively. However, even when these undesired compounds are not present or have already been removed by a pretreatment, the C -fractions are not directly suitable for some uses. 7

When the fraction is used as motor fuel or as heating material, high content of propylene are frequently disturbing, due to the tendency to form sootlike compounds.

If for example liquid hydrocarbons are subjected to pyrolysis besides the primarily desired ethylene also other unsaturated hydrocarbons, such as propylene, are always obtained. However, the ratio of the consumption of ethylene and propylene often does not correspond to the ratio of the formation of these two hydrocarbons in the pyrolysis, since the need for propylene is not equal to the quantity formed. Consequently, it is frequently desirable to use this C -fraction for the pyrolysis in order to produce ethylene therefrom.

We have now found that compounds with an olefine content provide substantially less satisfactory results in cracking than propane, and also cause an increased formation of cokelike deposits in the pyrolysis plants.

Thus, we have now found that the conversion of all unsaturated hydrocarbons in C -fractions containing unsaturated hydrocarbons can be carried out in a particularly advantageous manner by hydrogenation in the liquid state in a substantially static hydrogen atmosphere and in the presence of a catalyst fixedly arranged in the reaction chamber. In one preferred form of the process according to the invention the treatment of the C -fraction is effected in a so-called trickling phase, i.e. in a downward flow.

The starting materials used for the new process should consist substantially of C -hydrocarbons containing substantial quantities of propane, e.g. 30 to 95 percent. Other constituents which may be contained therein are, for example, propane and other unsaturated hydrocarbons such as methyl acetylene and propadiene. However, they may also contain fractions of lower or higher hydrocarbons, e.g. C or C hydrocarbons. it is desirable for the starting materials to be as far as possible free from hydrogen sulfide and carbon oxysulfide.

When using C -fractions containing relatively large quantities of highly unsaturated compounds, for example, methyl acetylene and propadiene, it may be advantageous for these highly unsaturated compounds to be transformed by known hydrogenation processes wholly, or at least to a major extent into propylene or propane before the hydrocarbon mixture is introduced into the reactor for the propylene hydrogenation.

ln a preferred form of the process according to the invention, a part of the hydrogenation product is returned to the inlet of the reaction chamber. This return is preferably ef fected without relaxation. of the pressure of the returned material, for example, from a separator which is connected after the reactor and in which the hydrogenation product is collected and separated from the gases. The quantity of returned product is chosen to be between 0.3 and three parts by weight of returned product for each part by weight of fresh product and advantageously one to two parts by weight for each part by weight of fresh product. In certain cases, it is desirable slightly to lower the temperature of the returned product before the introduction thereof into the inlet of the reactor. The throughput of fresh material through the reactor can generally be, for example, between 2 and 20 kg. per hour for each litre of catalyst volume, and advantageously 5 to 15 kg. The recycling of part of the hydrogenation product is particularly important in those cases where the C -fraction introduced contains methyl acetylene and allene as impurities. Thus, we have found that with the hydrogenation of such a fraction, normally obtained in pyrolysis plants, there is a relatively quick loss of activity of the catalyst if the hydrogenation takes place without recycling of product. When using the return flow, the catalyst maintains its activity for several months; even when a C -fraction free from these impurities is used, the control of the reaction and the maintenance of the reaction temperature are greatly facilitated by the return flow.

The hydrogen gas to be introduced should contain at least 50 percent of hydrogen. Hydrogen contents higher than percent are advantageous. The hydrogen gas should be as free as possible from carbon monoxide and also from hydrogen sultide and carbon oxysulfide. The quantity of hydrogen to be introduced into the reaction is measured in such a way that there is generally available an excess of 10 percent or more of hydrogen as compared with the calculated consumption for the hydrogenation of all unsaturated compounds. In general, it is not necessary for the excess of introduced hydrogen to be raised to more than 50 percent. On account of this small hydrogen excess, it is not necessary for the hydrogen gas to be recycled. in order to discharge from the system the foreign gases contained in the hydrogen gas which is being used, it is sufficient to release a small gas quantity at the end of the reaction chamber from the system after separation of the liquid hydrogenation products. This released gas will generally be introduced into the usually available gas separation plant in order to recover separately the constituents contained therein.

The process according to the invention is preferably carried out at temperatures between 10 C. and C. and advantageously from 20 C. to 50 C., it having proved desirable to allow the temperature to rise slightly during the flow through the reaction chamber, for example by [0 C. to 30 C. (from the inlet to the outlet of the reactor). The pressures to be used are advantageously controlled in such a way that they are sufficiently higher than the saturation pressure of the initial material being used at the temperature chosen. The hydrogen partial pressure should be at least 10 percent of the hydrocarbon partial pressure at the highest hydrogenation temperature employed. It is generally sufficient to have a hydrogen partial pressure which is not higher than the hydrocarbon partial pressure. Total pressures from 10 to 50 atm. gauge are suitable.

Noble metals in the VIIlth group of the Periodic System of the elements, mainly palladium and platinum, are suitable as catalysts for carrying out the process. These metals are used in quantities of about 0.05 percent to 2 percent and advantageously 0.1 percent to 1 percent on a support. Aluminum oxide, which may also contain relatively small quantities of other oxides, such as silicon dioxide, is for example suitable as a support. The aluminum oxides may have intrinsic surfaces between 5 and 300 m. /g. Aluminum oxide supports with surfaces of less than mF/g. are advantageously used. Supports which consist wholly or partially of aluminum spinel are also particularly suitable. Lithium, beryllium, magnesium, copper, manganese and nickel are of particular value as spinel-fonning metals. The proportion of spinel in the support is advantageously at least 20 percent by weight but as far as possible 40 percent or higher. Supports which have proved especially suitable are those in which the sup ort consists almost completely, for example, of 95 percent to 100 percent, of spinel. The spinels are desirably produced from highly active aluminum oxide with an intrinsic surface of from about 200 to 300 mF/g. which is transformed into spinels by reaction with the compounds of the spinel-forming metals. It is possible to use the aluminum oxide in lump form (small cylinders, pellets or balls), to saturate it with the solution of a compound (salts or hydroxides) of the spinel-forming metal which is to be used and to produce the spinel formation, optionally after intermediate thermal decomposition of the salt, by heating for l to hours at 900 C. to l,300 C. In a corresponding manner, it is also possible to start with finely powdered aluminum oxide of the same type and to effect the shaping of the catalyst after the saturation or salt decomposition.

The invention is illustrated by the following examples.

EXAMPLE 1 The catalyst support was constituted by a heat-treated aluminum oxide in small cylinder form with an intrinsic surface of 12 m. /g., to which 0.5 percent of palladium metal had been applied by saturating the cylinders with sodium-palladium chloride and precipitating the palladium with hydrazine hydrate. This catalyst was introduced into a vertically disposed tube having an internal diameter of 20 mm. and a length of 1,500 mm. A C -fraction was introduced, which had been obtained by separation of gases from the pyrolysis of light naptha. The C -fraction had the following composition:

aluminum oxide balls with an intrinsic surface of 230 mF/g. were saturated with a lithium hydroxide solution to such an extent that the saturated and dried catalyst support contained 1.2 percent of lithium. This support was heated for 8 hours to l,050 C., a 100 percent lithium-aluminium spinel being formed. 0.2 percent of palladium metal was applied to this su ort in the manner described in example 1.

e same C -fract1on as described 111 example l was used and the hydrogenation was carried out in the same manner. The product obtained consisted of 99.7 percent of propane and 0.3 percent of propylene.

EXAMPLE 3 A 'y-Al o in spherical form was saturated with an aqueous nickel acetate solution and heat-treated for 10 hours at l,000 C. X-ray analysis of this support showed: 85% of (X-A12O3 +10% of nickel-aluminium spinel +5% of a nickel-0x0 compound.

The support was saturated with an aqueous sodium-palladium chloride solution and washed and the palladium was then reduced. The prepared catalyst contained 0.6 percent by weight of Pd and 6.0 percent by weight of M0, the remainder being A1 0 Using the catalyst prepared in this way, hydrogenation was carried out with the CK -fraction indicated below. The apparatus mentioned in example 1 was used and the hydrogenation conditions were as indicated below. The conditions and the results of the hydrogenation are apparent from the following data.

% by volume Conditions Fresh throughput kg./liter-hour 5 Return of hydrogenation kgJliter-hour 5 Propane 4.2 5 product py Temperature (C.) inlet 40 Allene 0.5 outlet 60 Methyl acetylene 0.7 Pressure (atmgauge) 40 The hydrogenation took place at a pressure of atm. in a Results practically stationary hydrogen atmosphere, the material to be is t? g g gz treated being applied to the top of the reactor, trickling down progylene 94118 f in the hydrogen atmosphere over the catalyst and being Propadiene 0.55 o.0o2 separated from the gas in a separator below the catalyst bed. 01)":

The reaction temperature was 40 C. at the inlet to the reactor and C. at the end of the catalyst bed. The hydrogen input was regulated in such a way that 20 percent more hydrogen was introduced and correspondingly released at the end of the reactor than corresponded to the chemical consumption. From the hydrogenation product collected in the connected separator, twice the quantity, related to the fresh product introduced, was returned to the inlet of the reactor without release of pressure The fresh input was 7 kg. per liter of catalyst per hour. The hydrogenation product removed from the system had the following composition:

% by volume Propane 99.5 Propylene 0.5

EXAMPLE 2 The catalyst support was prepared in the following manner:

What is claimed is:

1. In the process for hydrogenating an unsaturate containing C aliphatic hydrocarbon fractions which may additionally contain small amounts of C and C hydrocarbons, in which such fraction is passed over a fixed-bed palladium catalyst on a support with an intrinsic surface of about 5 to 300 m./g. selected from the group consisting of aluminum oxide and an aluminum spinel, in the trickle phase in the presence of a reducing atmosphere predominantly consisting of hydrogen, the improvement for hydrogenating the unsaturated C hydrocarbon to propane which comprises maintaining the hydrogen content of the reducing atmosphere at a value of at least 10% in excess of the amount required for a complete hydrogenation and recycling about two to three parts of hydrogenation product per part of fresh feed to said hydrogenation.

2. The improved process according to claim 1, wherein the catalyst support is aluminum oxide.

3. The improved process according to claim 1, wherein the catalyst consists wholly or partly of an aluminum spinel. 

2. The improved process according to claim 1, wherein the catalyst support is aluminum oxide.
 3. The improved process according to claim 1, wherein the catalyst consists wholly or partly of an aluminum spinel. 